This invention relates to metal electrodeposition and more specifically to acid tin electrodeposition baths containing special brightener additive materials.
Acid tin electroplating baths for producing bright tin deposits are well-known and disclosed in the prior art such as U.S. Pat. No. 3,709,799, which patent is incorporated herein by reference. These baths generally contain sulfate, alkyl sulfonate or fluoroborate ions, a reducing agent such as formalin, a non-ionic surfactant, and as brightening agents an aromatic or heterocyclic ring-containing aldehyde wherein the carbonyl group is directly attached to the aromatic or heterocyclic ring or .alpha., .beta.-olefinically unsaturated carbonyl compound, such as benzalacetone. Other known brightening agents include 2-furylmethylketone and 1-naphthaldehydes. Secondary brighteners include polymerizable organic compounds capable of reducing the overvoltage for the evolution of hydrogen at a tin cathode such as acrylic acid, 2-vinyl pyridine, tetrahydrofuran and vinyl acetate.
Acid bright tin electroplating baths also known in the prior art contain a primary brightener of the formula X--CH.dbd.CH--Y wherein X is phenyl, furfuryl or pyridyl and Y is hydrogen, formyl, carboxyl, alkyl, hydroxyalkyl, formylalkyl, or the acyl radical of a carboxylic acid. Formaldehyde and certain imidazoline derivatives serve as secondary brighteners in such baths, especially when employed with non-ionic wetting agents.
A number of baths and additives are shown in U.S. Pat. Nos. 4,000,047 and 4,139,425, which are incorporated herein by reference.
U.S. Pat. No. 4,000,047 is directed to the electrodeposition of tin-lead alloys from aqueous acid fluoroborate, sulfamate and silicofluoride systems using pyridine and quinoline compounds as brighteners. The disclosed brighteners have no effect or a minimal effect in the acid-tin baths of the invention and, in some cases, have a deleterious effect. Only the 2-vinylpyridine-N-oxide disclosed at column 7 of the '047 patent is effective in applicants' tin--H.sub.2 SO.sub.4 bath.
Tin--H.sub.2 SO.sub.4 plating baths are important commercially and it is desirable that the quality and clarity of the tin deposit be improved. Also important is to increase the temperature range and operating life of the bath.
The present invention has among its objects the provision of an additive for sulfuric acid tin electroplating baths to provide enhanced plating performance and brightening effects, among other benefits.
A further object is to provide a method for tin electroplating using the baths of the invention.
Other objects and advantages will be apparent from the following description.